Posted
by
samzenpus
on Thursday December 25, 2008 @12:18AM
from the matthew-murdock dept.

iammani writes "The NYTimes runs a story about a blind man (blind because of a damaged visual cortex) successfully navigating an obstacle maze, unaided. Scientists have shown for the first time that it is possible for people who are blinded because of damage to the visual (striate) cortex can navigate by 'blindsight,' through which they can detect things in their vicinity without being aware of seeing them."

After some practice I could do it myself. So can you. Start with a hallway with hard walls and walk down it blindfolded using your ears. It may help if you make a high-pitched sound. (at least high-pitched sounds are easier for me) I can only avoid large objects that don't aborb sound myself, but I bet I could get better.

I don't doubt it all. Lots of people can. The brain automatically enlists your other senses when one of them isn't working. That's why I think the article is a just a load of BS. I don't think the man saw anything. I think his brain was just able to use his other senses to accomplish the same goal.

I would suggest having the blind man and an average-sighted man separately walk down a very well-lit corridor with randomly positioned (i.e., changing every iteration) obstactles 10 times, recording the amount of time each takes and the number of collisions. Reduce the amount of lighting by some increment and repeat the experiment. Continue reducing lighting until total darkness is achieved.

If the blind man is truly navigating by blindsight, both his course times and collision rates should roughly scale positively with those of the sighted man and inversely to the light levels. But then, that would be using the scientific method like the international team of neuroscientists in TFA (whom you are accusing of incompetence) did, so of course you wouldn't believe it...

From TFA:========They include place cells, which fire when an animal passes a certain landmark, and head-direction cells, which track which way the face is pointing. But the new study also found strong evidence of what the scientists, from the Norwegian University of Science and Technology in Trondheim, called 'border cells,' which fire when an animal is close to a wall or boundary of some kind.=====I suspect this is the same phenomenon as those 'border cells'

The article sure reads like BS, but that's popular science for you. I read about this kind of thing back in first year psychology (never did second year, I don't claim to be an expert). The brain is, frankly, a complete fucking mess from a design perpsective. It's entirely possible to knock out random parts of abilities that would be unitary if the brain was well designed, particularly through strokes or other injuries that damage small parts of the brain exclusively. Speech centres are classic; people lose

Full disclosure: I was born 3.5 months premature, and my retinas detached at 4 months.

I call it being able to hear the "sound shadows" of objects, because that's really what they are - an object blocks sound, and that blockage is projected to the ear. With a good cane, I can navigate around tables, columns, and even position myself relative to peoples' voices to keep myself from running into them. It's quite amazing what you can tell with a good hallway, and a constant sound source (soda/vending machines are good). For example, an open, echoy space usually means a stairwell.

Also, randomness... the first time I went to post, my screen reader [gnome.org] was very sluggish and crashed. I guess Slashdot hates blind Linux users.

That's very cool. It's also proof of how amazing the brain is - the part that makes a 3D model of your surroundings will adapt to any sort of useful input. With just sonic shadows you're working with very limited data, but even so: the navy has spent a ton trying to develop good passive sonar, and it sounds like you're better at it than the technology. Now if someone could just invent a sonic lens, it would close the gap. The only reason light gives better 3D positional information is the lens (though it would also be helpful to hear sub-millimeter wavelengths, as 20 kHz doesn't give much precision).

Sighted people can learn this, too. I worked in an office where I had my back to a doorway, and through that door was a room full of servers. No one was ever able to sneak up on me because I could hear their sound shadow as they walked by the servers. It took me a while to figure out how I was aware of them, because it wasn't really a conscious thing at first.

Agreed! Although I am fully sighted, from childhood I would practice walking down dark hallways with eyes closed. The "sound shadows" you describe are only a part of it - an analogy that the sighted can grasp.

Local changes in reflectance and absorbance of sound as you navigate a 3-D space are also richly informative as to the shapes and types of surfaces around you, in addition to their locations. It is particularly powerful in a space with which you are familiar, like your home.

While that is true, that's not what's happening here. In the case from TFA, the man is not conscious of any visual sensory input, but IS able to subconsciously make use of visual information. Also from TFA, he has the same subconscious responses to being shown pictures of people's faces displaying various emotions and other responses that cannot be due to echolocation.

In another experiment (not part of TFA) a number of subjects with cortical blindness were able to accurately state which direction a dot of l

It may help if you make a high-pitched sound. (at least high-pitched sounds are easier for me)

The higher the pitch, the closer the wavelength, and at the distances we're talking about (centimeters to meters) you're auditory system will be doing localization with phase differences and wavefronts instead of actual "echo," since the time delays on echo are pretty hard to pick up on so close to the listener (believe it or not, but your ears-brain loop is extremely sensitive to phase differences between the two

Without a working visual cortex, nothing from the eyes enters the brain. At all.

It would be really nice if hypothesis and biology worked like that, where biology followed our hypotheses, but it doesn't. It would be interesting to see an fMRI, or see if he could navigate the maze with earplugs or some way of throwing off air pressure. Assuming it can't possibly be his eyes connecting to some other part of the brain simply because textbooks say the eyes connect only to the visual cortex is not a safe conclusion.

Most likely those subcortical connections are there as a link to the reflex system. High level visual processing would likely take too much time to process for reflex action. Damage to the subcortical links but not to the visual cortex would likely make for someone that's slower to react to visual stimulus and very clumsy.

I've seen a thing in the vein of those "reaction test" games, where you click as soon as a dot appears on the screen. But the 5th dot in the set is much bigger than the others, so it triggers your startle response. Cut my reaction time almost in half.

Makes sense really - if something jumps out at you, you don't want to be waiting for the conscious mind to come up with a solution when a reflex response could already be happening.

"Without a working visual cortex, nothing from the eyes enters the brain. At all."

Whoopsie. Apparently you didn't know about the body of work showing that there are connections between the retina and subcortical areas as well as the striate cortex. Of course, if you'd read the article, you would have noticed they mentioned that.

Yes, I read your other comments, including the one where you claim to have read the article. To summarize: you don't think it's possible... because .

Actually, if you look at the video found here [blogspot.com], you'll see that your theory of human echo-location is totally inadaquate to describe what he is doing -- he avoids the walls, but also an overhead projector on the floor and some really small items.

If you RTFA (I know, a big assumption -- Google can take you to the no-registration-required SciAm version), they say that scientists suspect there are other pathways where the info is getting into his brain, even though his visual cortex is totally destroyed on both hemispheres. This is the first blindsight demo with NO visual cortex, and thus seems to suggest strong that there are some alternate pathways going on. He can also react to facial expressions.

"No, he's not. Without a working visual cortex, nothing from the eyes enters the brain. At all. Most likely, he is using sound or air pressure."

The signal from the optic nerve doesn't go exclusively to the primary area of the visual cortex- it forks at the lateral geniculate nucleus before it gets there and some also goes to subcortical targets which provide functions like the flinching reflex. These are older pathways and modern vision evolved by eavesdropping on the signal.

"Without a working visual cortex, nothing from the eyes enters the brain."

Technically the eyes are part of the brain. The visual cortex is brain jelly (mammalian GPU, one per eye, crosswired), perhaps you were thinking of the optic nerve. Nobody is claiming this is a "sixth sense", it's another part of the patients brain doing primative visual processing. Very similar to how some stroke patients have to learn to speak all over again.

Or, you could read the article, which points out that the retina sends signals to both the visual cortex AND some sub cortical areas. While his visual cortex was inert, the sub cortical areas were not, and based on this research they've determined that they can function independent of the visual cortex, and it appears they also perform some specialized visual functions such as facial expression recognition. This has been demonstrated in other animals, this was the first time it was confirmed in humans.

"Without a working visual cortex, nothing from the eyes enters the brain. At all. Most likely, he is using sound or air pressure."

I'm sorry but that's completely incorrect. Light enters the eyes, hits the retina, is converted to an electrochemical signal, sent out the optic nerve, passes the optic chiasm, then heads back to the lateral geniculate nucleus of the thalamus. Most of the "signal" goes back to V1 in the occipital lobe but some signal also goes to the hypothalamus, superior colliculus (on the br

Maybe the problem is that TFA tried to make the science more approachable to people, but you obviously don't understand a single thing about blindsight. This is nothing new at all. In layman's terms, the participant still experiences visual sensation but not visual perception -- they can still see, but they are unaware of it. What is significant in this case is the extent of the damage to the visual cortex. The sensory compensation of congenitally blind people is incredible, but this is an entirely different phenomenon.

Sight doesn't "occur" in the eyes, but there are a number of subcortical structures the information passes through before it gets to the visual cortex. Which, oddly enough, is exactly what they say in TFA, which you claim to have read. They specifically say that the "visual areas of the brain" did NOT "light up", so I have no clue what you're babbling about.

The entire point of the article is that the extent of subcortical visual processing (which we are unconscious of) is greater than most people realise. So feel free to read it again and appreciate what is actually a well-established neurological phenomenon.

IMHO, sight doesn't happen as much in the eyes as it does in the brain.

Well, that's how the brain does its thing. Your eyes, ears, nose, skin, are instruments that extend from the brain. Data that flows from your senses to your brain lacks meaning until the brain processes it.

Data still flows from the eyes over the optical chiasm to the primary visual cortex (the cortex around the calcarine fissure in the occipital lobe). From there, there are multiple "streams" of visual data. One of those streams is the one that "enters" consciousness.

It is the absolute certainty with which you refute the previous, and the postulation of the following near-superhuman senses that make you appear rather uninformed and quite arrogant.

Most likely, he is using sound or air pressure. Blind people can often maneuver by hearing things like subtle changes in sound of footprints, etc., echoing off of or being aborbed by walls, etc. There are also subtle changes in air pressure as you approach obstacles, and that can often be 'felt' by blind people.

Take a biological psychology course or your own medicine (your signature)

Doctors remain baffled at the inability the majority of Slashtards to read and comprehend a simple article summarizing a medical experiment, despite apparently functioning visual systems. "They just wouldn't quit insisting that the subject of the experiment used echolocation to navigate the obstacles in the hallway, no matter how clearly and explicitly the article explained that the possibility had been ruled out," say baffled researchers. "We don't think their brains are wired correctly."

Whoever tagged this "badscience" should take an introductory neuroscience course sometime.

For those whose curiosity hasn't entirely been replaced by fashionable knee-jerk skepticism, your optic nerve does not only terminate in what we think of as primary visual cortex, it sends projections to other areas as well, though these areas do not contribute to what most of us think of as "sight"

It should be no surprise that a blind man can navigate a maze. Blind men have successfully navigated mazes faster then others for quite a while.

That's because their navigational algorithm is much simpler. put your hand on the right wall and follow it.

You'd be surprised how much easier things can get when you eliminate useless data. This, however, seems to be a more noteworthy experiment in that it was more than just a regular old maze with two ends.

This is hardly the first time blindsight has been demonstrated. I recall Ramachandran at UCSD doing experiments on it a while back.

One of the more mind blowing things I read in 2008 was the discovery of a third type of visual receptor besides rods and cones. Essentially there's a third type of receptor that only detects sort of gross levels of light, and feeds directly into the system which regulates your circadian rhythm and is used for some other purposes. People that were completely blind were able to tell when light levels were fluctuated in a large way, like walking in front of a TV, and be totally puzzled how they knew that, since it didn't register as sight at all for them.

The fact that these neuroscientists would call it the first evidence for blindsight means that either they really didn't read their papers very well, or it was a bad article summary on Slashdot.

Those are the photosensitive retinal ganglion cells. In addition to driving the circadian rhythm generators, they also control pupil size in response to light. IIRC, research in cats found that they do connect to the visual cortex, although how the signals are perceived is not yet known.

Yeah, those. The really interesting thing is that people have been dissecting human eyes for many, many years without noticing them before.

While they may connect to the visual cortex, there is no perception of light from the

My daughter had a stroke before she was born, and as a result, she suffers from Cortical Visual Impairment (CVI), like the subject of this story. At nine months of age, she couldn't tell light from dark, which really screwed up our sleep cycles. Her eyes were fine, but her brain could not process the signals that they were sending to her.

Eventually, she did regain some amount of vision, but her hearing is still her primary way of "seeing" things. Whenever we go into places that are pitch dark, my wife and I are walking into things left and right. My daughter, on the other hand, cruises right around like a bat. She hears walls and other obstructions, and corrects her course to avoid them. Her object avoidance skills greatly diminish when she can use her eyes to see, as her brain has to work much harder to decode what she sees with her eyes.

My daughter, who is now four years old, is very attuned to large spaces that echo. She can hear them coming and as she approaches, she usually shouts "Ha!" to hear it come back to her.

That being said, she doesn't need to click her tongue to sense walls and such. Even in quiet rooms, there is enough ambient noise from her motion and things around, that she can sense the location and more importantly the nearness of objects. When she "looks" at something, she is rarely looking straight at it. She lowers h

She may also be sensing air currents with the fine hairs on her face and neck.

One of the ways you can readily spot a blind cat is that it will ALWAYS keep its whiskers stretched forward -- not to touch things with, but to sense micro-currents that surround objects, so as to avoid running into them. These cats can be good enough at it that their owners won't believe the cat is blind. I once had a very old cat who was both totally blind and stone-deaf, and he navigated entirely via this whisker-based "air sen

I'm not surprised by the fact that her poorly processed vision can actually be a hindrance at times. Personally, if I try to walk through an unfamiliar dark room (whether it's really dark or my eyes just haven't adapted yet), I'll fumble around and walk haltingly. If I close my eyes, it's like my brain "gives up" on trying to use the eyes, and much of the weirdness goes away. I may still walk into things, but I'll do it with confidence.

I think your daughter might be better off just closing her eyes when the

There are two distinct causes of blindsight (and deafhearing and alien limb syndrome), damage to the primary sensory cortext but not the secondary or assosiation cortices, and damage to the association cortex, but not the sensory.

The latter is easy to explain. The person can perceive, but can't incorporate the fact of it into their conscious experience. They can't "own" the perception. This is very often found in damage to the somatosensory cortex which leaves partial paralysis. Often the person can't perceive the limb attached to their body as 'theirs'. Sensations in the limb do not become perceptions for them. Similarly, vison and hearing can occur, and the brain can make use of the data, but the person can't perceive it because it's not coming from "them".

The former is harder to explain. There seems to be a parallel visual (and auditory) system through which information can pass and the brain make use of, but which bypasses the association cortex. The person can't perceive normally, but if tested they react as if they can. They can, for instance, consistently "guess" the number of fingers shown them. There is a similar system for somatosensory. Perception of touch to, say, the hand, has highly detailed "maps" elsewhere on the body. For the hand it's on the cheek and on the back just below the shoulder. Just why this secondary pathway exists is a mystery. But it does, in most people.

Around 20 years ago in Coevolution Quarterly there was an article about a 'school' in (IIRC) New Mexico that taught people to use their blindsight to navigate in the desert at night. The secondary visual pathway that persons with the second form of blindsight use, exists intact in everybody. It's not something you develop because of damage, it's something that's there in case you need it but below the level of consciousness so as not to interfere with normal perception. Occasionaly hunters, hiker/campers or survival technique practioners will hear of a person who can literally run through a pitch black forest without running into anything. These people have the ability to react to the subliminal perception from the secondary visual system in what occurs to them as instinctive reactions because they don't consciously perceive anything.

There's also other differences as well. Some women, for instance, have see a fourth set of colors, which gives them a much greater low-light ability (a couple for every thousand women, IIRC) as well as do great things in the visual arts. Other people have vision that extends a bit beyond the normal ranges as well. A good example if this is the typical "normal" body temperature. It was obtained by sampling a large number of people and averaging the result. Vision, hearing, and other senses are similar. So it's not surprising that the occasional blind person can actually tap into these if theirs happen to naturally be more developed than normal.

By tapping into the secondary pathways like this, I can "see" about twice as well as most people in the dark(though it's not really "seeing" like reading a paper or like a cat does). And, as DynaSoar mentioned, I can literally run through areas at night and not hit things as long as there is even a tiny amount of light.(doesn't work in caves/absolute pith black - tried that - heh)

Note - the skill can be learned, though some see better at night than others. I suspect their vision is shifted a bit more towards the infrared or their iris' are a bit larger. It took me about 2-3 years to develop it when I was growing up. My friends and I always spent a lot of time playing outside at night and some of us got pretty good at avoiding things in the dark. The hard part was learning to just trust your instincts. It's a odd feeling, though, as you only notice things a split second before you normally would hit them if you're moving faster than walking speed.

I found that a trick to doing this - and you can try this as well - is to learn to defocus your eyes during the day. Animals do this to track movement. It's a common trick hunters also use to track and find game. If you can then also do this at night, it basically shuts off a lot of your brain's trying to strain itself in low light. Since the average person's brain normally focuses intently upon just a small area in front of them, expanding that to your entire field of vision makes a huge difference.(though as noted, you can't focus on specific objects at the same time) Often, even if you can't actually see details, your eyes will notice things like faint reflections, movements, and so on.

My ex? She's nearly completely blind about 5 minutes after dusk. Opposite end of the scale as it were.

Plekto, are you reading my mind? I purposefully withheld mention of my own night vision. You supplied not only details of it, but of how I developed it. Your accounting tells the tale so exactly it's almost spooky. But given the mind that I have, it ends up as considering how much more likely I am to be able to find and test enough people in a similar task in order to determine why some have this and others do not.

One point of contention, there are not "some women that see in 4 colors". There are some peopl

The same visual technique can also be used to spot dim satellites. Start out fully de-focused looking over the entire sky. Before long, you'll feel an 'urge' to look to a particular place. DO NOT do so. Instead, look near that point but not quite focused. Then you can see the rather dim light moving slowly against the background. It may appear to blink out occasionally if you let it get too close to your central vision (it is a constant brightness, the blinking is a visual artifact).

The same visual technique can also be used to spot dim satellites. Start out fully de-focused looking over the entire sky. Before long, you'll feel an 'urge' to look to a particular place. DO NOT do so. Instead, look near that point but not quite focused. Then you can see the rather dim light moving slowly against the background. It may appear to blink out occasionally if you let it get too close to your central vision (it is a constant brightness, the blinking is a visual artifact).

It's also how those with very good or well corrected vision can see Mizar's visual double Alcor (the star in the center of the Big Dipper's handle). The separation is enough, but Alcor is much dimmer and difficult to perceive, especially with current levels of light pollution.

It's not the same. I've been an amateur astronomer for over 4 decades and am very familiar with the technique. It's based on the fact that the more light sensitive rods are squeezed out of the central visual field by the color sensitiv

It's not the same. I've been an amateur astronomer for over 4 decades and am very familiar with the technique. It's based on the fact that the more light sensitive rods are squeezed out of the central visual field by the color sensitive cones, making things only a few degrees off center appear brighter. The off-center technique still results in conscious perception. Blindsight/night vision does not. OTOH, that makes night vision suck for astronomy; it does no good to look if you don't know you're seeing it.

It isn't exactly the same, but the part of finding the satellite IS based on the alternative visual pathways. The rest is significant training of both conscious and unconscious pathways to prevent attempts to track to the center of vision.

Beyond potential for rehab, the big reason neurophysiologists are interested in blindsight is that it affords the opportunity to map out which part of the visual systems does what for us. Very few people are even aware of it at all other than having visual perception. Sail

[blink] I'm a little nearsighted (20/40 and 20/80) but I can see that double star without even thinking about it. With correction, it's perfectly evident.

However, I'm one of those freaks with obscenely precise colour vision; I also see VERY well in the dark (and tend to see better by looking straight at something than by the "not quite at it" technique). I suspect the two abilities are related. -- Conversely my neighbour, while not per-se colourblind, has poor colour vision with some deficit in yellow, and

Mate, you're not tapping into anything. Everyone has varying night vision - it all depends on the number of rods you have on your retina and how well your eyes adapt to low light. So give it up with the night vision powers BS , you don't have it.****

The "trick" here is to use more of your eye consciously by de-focusing enough so that you block out the horribly distracting and bad in low light fovea(center of your vision). Think of it as learning to utilize more of the data that is coming into your eyes. P

Occasionaly hunters, hiker/campers or survival technique practioners will hear of a person who can literally run through a pitch black forest without running into anything.

Actually, that is a combination of using other senses, stepping in a way that allows you to adapt to unanticipated terrain, and learning a different mode of vision that avoids tracking objects of interest with the fovea (which provides detailed color vision but is less sensitive to low light than the peripheral vision). I've done it many times.

It doesn't have to break the laws of physics! Your conscious vision is concentrated around the point you focus on. That is, you're throwing out some of the data about light surrounding that focus point. That doesn't mean it's not there!

If you ever want to see this in action, there's a very simple experiment you can do. Put a quarter inside a ring of five loons (Canadian $1 coins). Put another quarter inside a ring of five dimes. The quarter surrounded by dimes will look larger than the other one.

Reach out and pick one up. Put it back. Pick the other one up. Put it back. You'll notice that even though your eye is telling you the two quarters of different sizes, your fingers will automatically spread out just the right amount to pick up either coin.

The illusion works for your regular visual system. The unconscious one gets the answer right.

...the brain has a layered architecture. The more primitive brain has its own visual processing system. Evolution has built connections with this system and the parts of the brain that deal with awareness. Lose this connection and you can still "see", but not be aware of them (at a very high level).

It is not mentioned very clearly in the NYT article, but it is mentioned in the original Current Biology paper: this patient has BILATERAL lesions in both the left and right visual cortices. IMO, this is what makes this case especially interesting.

Of course, blindsight has been demonstrated many times before, but always in patients with unilateral lesions. This has some methodological advantages (the patients can act as their own control), but the unilaterality has also been criticised. Maybe these patients

Everyone knows that blindsight is an extraordinary ability, which can be used to operate effectively without vision. It might be a form of sensitivity to vibrations, acute scent, keen hearing, or echolocation. It even makes concealment and invisibility (even magical darkness) irrelevant to the creature with blindsight.

Well they said they found no evidence that he was, I'd still like if they elaborated that they gave him earplugs or something, even footsteps could give him enough audible info to navigate.

Ideally I'd like some mention of a control using a blindfold or something. From the sounds of it he wasn't truly blind, the eyes worked fine but signals either weren't getting to the brain, or weren't getting processed by the visual cortex. They seem to be suggesting the visual info is still somehow being processed to aid

And one would assume that you could demonstrate it in some way, maybe tell us something you saw that you couldn't otherwise see while under scientific scrutiny, and do so with a greater-than-chance frequency.

'cause y'know... if it's real I would assume that it's measurable or demonstrable in some way, otherwise the simpler explanation is that you're having a very vivid dream.

I know similar studies have been done and I'm still waiting for the one that will make scientists realise they've been wrong all a

For as long as I can remember, I've been able to tell when I was near a wall in a dark room, or with my eyes closed. I don't know if I'd describe it as sonar per se, but I can also tell if someone is standing close to me, no matter what our relative positions are.

FWIW, the last time I tested it with a tone genererator, my hearing topped out somewhere around 25Khz. I'm sure it's far lower now, but I can still tell if there's a CRT monitor powered on anywhere within fifty feet of me or so.

CRTs tend to make noise at the frequency of their horizontal sweep, due to EMF from the changing magnetic field in the deflection yoke. For a TV, that would be 15.75 Khz. There would also be some noise at lower harmonics of that frequency.